Leopard cannot change its spots - A.
You reap what you sow Link to proverb.
Let well alone.
When the oak is before the ash, then you will only get a splash; when the ash is before the oak, then you may expect a soak.
An army marches on its stomach.
You can lead a horse to water, but you can't make it drink Link to proverb.
Needs must when the devil drives Link to proverb.